I've run into an odd problem I can't figure out.   I'm working on a 3D model project that will be a sort of construction kit made up of various wall sections.  Things have been going well and I'm almost done modelling the first set of props.  I have been importing them to Poser for test renders using some default stone MATs just to get an idea how the props looks.  Below is an early test render with V4 included for scale.

As you can see everything rendered fine, all the textures are various default stone MATs that came with Poser.  The walls are UV Maps, single sided, normals all correct, no doubl vertices.

Tonight, while doing some further test I suddenly got an odd color problem on a wall prop that had previously rendered fine.  I have not altered the UV map or the vertices, I simply re-exported it.   What is more puzzling is this color issue only seems to happen with this one marble MAT, I can use the granite MAT and it renders fine.

So my quest is, any idea what is causing this?  Or why it suddenly appeared when it had previously imported and rendered fine?  I'm creating these in Blender, exporting in OBJ format and importing to Poser 6.